Wind Energy

Relative Power and Loading [%]
61 On the Influence of Low-Level Jets on Energy Production 327
130
125
120
115
110
105
100
95
1.5MW_Power_A 1.5MW_FlapSTD_A 1.5MW_Tilt_A
1.5MW_Power_B 1.5MW_FlapSTD_B 1.5MW_Tilt_B
5MW_Power_A 5MW_FlapSTD_A 5MW_Tilt_A
5MW_Power_B 5MW_FlapSTD_B 5MW_Tilt_B
90
85 90 95 100 105 110 115 120 125 130
Hub Height [m]
Fig. 61.1. Influence on power, standard deviation of flapwise bending moment and
mean tilt moment for Scenario S1
The effect of this scenario is shown in Fig. 61.2. It can be seen, that the
presence of a LLJ leads to much higher differences then in the previously
examined situation. The difference in power output in the case of the 5MW
turbine with 130 m hub height is almost 30%, while the difference in the blade
bending moment’s standard deviation is up to 25%. The general tendencies
that have been observed before remain unchanged: the relative differences are
higher for the 5 MW turbine and for profile A.
61.4 Conclusions
The main conclusions that can be drawn from the analysis are as follows:
– LLJs have clearly an impact on the turbines performance. They lead to
an increased power output and standard deviation of the blades flapwise
bending moments
– The influence of LLJs increases with turbine size
– The error in estimating the turbines performance can be quite high, up to
30% in the investigated cases, when the mean wind speed at hub height
needs to be calculated from some height below
Regarding the influence of LLJ on life time calculations, it has to be considered
that life-time fatigue loading and annual energy yield depend directly
on the site-specific frequency of occurrence and severity of such events. Therefore
their impact is hard to estimate but will probably be small. This is mainly
due to the fact that at least at the measurement sites, these situations did